This section provides background information related to the present disclosure which is not necessarily prior art.
Sport-related concussion is understood to be a significant public health concern which may be underreported. Studies have suggested that >5% of high school and college football players sustain a concussion during a single season. An athlete who has sustained an initial concussion is more susceptible to repeated concussions, and the athlete with multiple concussions is at increased risk for abnormalities in neuropsychological testing and ongoing symptoms. Premature return to play is of particular concern to society in general, and it appears to be associated with increased likelihood of further injury, prolonged experience of cognitive symptoms, and even death on rare occasions. The last concern refers to the “second impact syndrome”, a catastrophic outcome in child and adolescent athletes.
Prolongation of reaction time after sports-related concussion has been recognized for many years. Importantly, concussed football athletes have shown impairments in reaction time as compared to controls several days after complete symptom resolution and clearance to return to play. However, present practice for determining reaction time typically includes a personal computer and specialized software-equipment not usually immediately available because of the associated cost (typically $500 per football team per year)—and is not available to the great majority of high school, and younger, athletes. This is especially important given evidence that the adolescent brain, as compared to that of the adult, is more vulnerable to sports-related concussion.
Reaction time can be partitioned into three intervals: a) Pre-motor time: from the onset of the stimulus to the onset of increased myoelectric activity in the response musculature; b) Electromechanical delay: from the depolarization of the response musculature to the acceleration of the response limb; and c) Movement time: from the initial acceleration of the response limb to completion of the task. A prolongation of any of these intervals can increase reaction time; e.g., a delay in upper extremity limb acceleration was the major source of delay in older women asked to move their hands quickly into position to break a fall. In some examples, a clinical reaction time can be defined as a measure of the speed with which a functional task relevant to sport, prevention of a blow to the head or face, is performed. However a clinical measure of reaction time would be of greatest use in evaluating sports-related concussion if it measures pre-motor events, since that interval includes central neurologic processing time.
Scientists define at least three types of reaction time including simple reaction time, recognition (or “Go/No Go”) reaction time, and choice reaction time. Simple reaction time (SRT) is the reaction time obtained when the subject has to respond in a similar way to the same stimulus. In one example, one could obtain a simple reaction time by simply dropping an object at random intervals and asking the subject to catch it each time as quickly as possible. The time taken to catch the object from when it was dropped is the SRT. No decision-making is involved by the subject. Recognition reaction time (RRT) is the reaction time obtained when the subject recognizes the presence/absence of a stimulus at the time the object is dropped and takes the appropriate action as quickly as possible. So in one example, the subject will have been asked to catch the object that is dropped using a pinch grip if a light comes on, but to let it drop if the light does not come on. Here the stimulus to catch the object occurs only intermittently and a decision has to be made as to whether to catch it or not. Choice reaction time (CRT) is the reaction time obtained when the subject interprets the stimulus that is presented at the time the object is dropped so as to make one of at least two different responses as quickly as possible. An example would be that the subject is asked to catch the object when it is dropped using their thumb and first finger if the light is green, but with their thumb and third finger if it is red. Here the stimulus varies, every trial and subject is burdened with making the choice between the two different motor responses or catching actions when responding to the stimulus as quickly as possible. It is known that the reaction time (RT) increases as a function of the number of choices according to the formula RT=a+b log2(n+1), where a and b are constants representing the intercept and slope of the function, and n is the number of choices.
Therefore an inexpensive clinical measure of reaction time would be welcomed in the evaluation of sports- and age-related neurological disorders or conditions, including sports-related concussion. Moreover, such a measure would be of even greater use if it was found to predict a sports-related protective reaction time (SPRT). The immediate availability of this information could influence return to play decision-making, and prevent repeat sports-related concussion or other injury.